Underwater Blasts

Cloud formation in underwater tests Baker (fat man design) Bikini Atoll 1946; 23 kT Formation of spray dome & condensation cloud from erupted water

First Moments  Eruption through water surface  Formation of spray dome (4 ms)  Spherical cloud condensation (1 s)  Break through of erupted water  formation of base surge (2 s)

The formation of surge & cloud Cloud development Surge development

Cloud expansion & fallout

Cloud Evolution

The Baker test The closest ship to surface zero was the USS Saratoga. Eight ships were sunk or capsized, eight more were severely damaged. Sunk vessels were the USS Saratoga (2 being hit by 90 ft wave, 3 front being swept by wave), USS Arkansas, the Nagato, LSM-60 (obviously), the submarines USS Apogon and USS Pilotfish, the concrete dry dock ARDC-13, and the barge YO-160. These were the first "weapons effects" tests ever conducted - tests designed specifically to study how nuclear explosions affect other things - rather than tests of the behavior of a weapon design (as was Trinity). The purpose of the tests was to examine the effects of nuclear explosions on naval vessels, planes, and animals. 2 3

The damage to the Atoll by Baker and subsequent tests - Bravo Atoll before the Bravo test Atoll after the Bravo test Population had been removed, numerous tests followed until the early sixties Entire island is contaminated with radioactivity; population is still not allowed to return: 2001 the US government granted $563,315,500 reparations to the Bikinians. For details see:

Underground test procedure Underground tests required careful preparation and monitoring. Hole depth and diameter are dictated by anticipated yield. Depth range: 600 – 2200 feet Diameter range: 48 – 120 inches Containment of radioactivity in hole is required; geological survey is necessary prior to test.Hole is stemmed after device is positioned. Underground cavity forms after explosion. Cavity drops forming chimney. If the strength of chimney is exceeded by weight of overburden, chimney collapses forming a crater.

SEDAN Preparations & Success 1962 Test to investigate “peaceful applications such as large scale construction efforts  Harbor building  Mountain removal

Underground test In underground tests most of the released energy goes into crater formation. Only a fraction of the energy goes into blast depending on explosion depth. The shape of the crater depends on depth of explosion; new applications are bunker breaking small nuclear weapon developments. Crater volume: V c ≈10 5 ·W m 3

Sedan test parameters and results  The 104 kT thermonuclear device was buried 635 feet below ground level.  The force of the detonation released seismic energy equivalent to an earthquake of 4.75 magnitude on the Richter Scale.  The blast moved 6.5 million cubic yards of earth and rock up to 290 feet in the air.  The resulting crater was 1280 feet across and 320 feet deep.

Crater formation in underground test Blast vaporizes material within radius r=2·W 1/3 m (W in kilotons (kT) of TNT) Blast melts material within r=4·W 1/3 m Blast induced seismic shock crushes material within r=50·W 1/3 m Gas release and seismic waves cause eruption and crater formation. Crater volume V c ≈10 5 W m 3. (Example Sedan ~10million m 3 )

Nuclear Cratering

Crater Building

Nuclear Bunker Busters 1 kT bomb 1 m underground (R s =1m) would have same effect as 35 kT bomb 1 m above ground. Or 10 kt bomb 2 m underground would enhance explosion yield by a factor of 20. (R s =0.9m) Shock enhancement for the explosion of a W kT nuclear bomb as function of depth. Scaled burial depth At low depths most of released energy is lost in blast rather than translated into seismic energy. Needs to contain most of the released energy underground to break structure by underground shock and energy release (no air venting). Underground structures are difficult to break, even by surface nuclear explosions. Underground explosion cause ground motion and seismic shocks.

bunker breaking nuclear missile systems New dreams of the pentagon to address the perceived threat from third world underground “terrorist” bunker systems.

Penetration limits 2-4 m penetrating depth of missile, most of energy is lost in release to atmosphere rather than in seismic shock, material liquefies at impact. 240 kT conventional warhead

Depth Length Impact Velocity Typically ~900 m/sec = 2700 ft/sec Long Rod Penetration versus Velocity B61-11 A needle 12 ft long 12 inches diameter Falling from 40,000ft height penetration depths was 20 ft

Chances ρ: density Y: material strength If penetrator material is 2x target material the depth to length ratio is 1.4. A 12 ft long missile penetrates 17 ft. Significant enhancement in material strength is necessary to improve beyond present means. (factor 100 in material strength and factor 10 in density would reach penetration depth of 46 ft only. B61-11 has special hardened nose.

High Velocity Kinetic Penetration A GBU-28 undergoes a high-velocity sled test, penetrating several meters of concrete.

Containment of nuclear blast Containment depth corresponds to explosive yield W. Present standard 300 kT earth penetrating warhead would need to penetrate to 500 m (instead of 20 m) to fully contain the energy underground. Even 0.1 kT warhead needs a 40 m depth for containment. Natural limit of penetration (set by deformation and liquidisation of penetrating missile ~ 20 m

Bomb test characteristics The effects of Nuclear weapons Blast damage Thermal damage Radiation damage EM-pulse Scaling laws Protection and shielding Distance effects Fall-out Atmospheric distribution Effects on population Radiation effects Fallout conditions Short range Medical consequences Long term medical consequences